Aircraft such as aeroplanes can generate considerable noise during a landing approach i.e. an approach to land. A significant portion of this noise is attributable to air flowing around the deployed landing gear and/or high lift devices such as flaps and slats.
Although during a landing sequence an aircraft may be travelling at around 80 s, the localised airflow around a noise-inducing component or region of the aircraft's airframe and landing gear may reach speeds of around 300 m/s; this can result in sound energy of around 200 W being dissipated as noise. The noise can be tonal, such as the whistling noise due to airflow over a cavity, or low frequency booming from wing boxes and panels, or broadband noise i.e. noise over a wide range of frequencies. Noise from turbulent airflow around the aircraft and wake turbulence is significant and the airflow around the aircraft, especially that circulating the wing, can cause elements of landing gear and high lift devices to vibrate, and these vibrating elements may in turn excite other elements of the aircraft such a wing boxes and surface panels; for example, landing gear doors. The above-noted types of noise are known in the art, and will be referred to herein, as aeroacoustic noise.
Aeroacoustic noise is undesirable because of the fact that airports are often located close to cities, or other densely populated areas. Aeroacoustic noise due to the landing gear and high lift devices is particularly problematic because it is radiated directly to ground due to the position of the landing gear under the aircraft and the high lift devices at chord wise extremities of the wing i.e. the leading and trailing edges of the wing.
Attempts have been made to address aeroacoustic noise problems. For example, it is known to provide an aircraft landing gear with fairings. A fairing is a generally rigid structure, often made from metal or composite materials, that is arranged to shield a noise-inducing region of an aircraft landing gear from airflow during landing. However, the present inventors have identified that known noise reducing devices, such as fairings, can undesirably increase the total weight of the aircraft. Moreover, known noise reducing devices, such as fairings, can undesirably increase envelope of aircraft components, such as the landing gear and/or high lift devices, and may affect articulation thereof. Fairings and the like can also affect cooling of components, such as brake parts, and are generally directional meaning that they may not be effective in crosswinds.